Resolution dropdown, list-focus preservation, unified dark theme, startup logging, and memory map

- Bottom-bar resolution dropdown (1080p60/1080p30/720p60/480p30) with tooltip
  on finding upload bandwidth; disabled while live; no in-app speed test
- FocusPreservingListBox keeps selection/focus coherent when a selected
  scene/source is deleted (skip hidden scenes; leave list when empty)
- Themes/Controls.xaml: single dark-theme dictionary merged once in App.xaml;
  custom ComboBox template fixes SelectionBoxItem rendering; GoLiveWindow and
  ReuseImageDialog consolidated onto shared styles
- AppLog file logger + AppDomain/Dispatcher exception hooks; checkpointed
  MainWindow/VM/dialog constructors (caught MenuItemRole.Separator XAML crash)
- Memory map: schema.md conventions, per-directory index.md, updated ai.md/
  TASKS.md/README.md (OAuth creds real; token persistence still pending)

ViewModels/MainViewModel.cs

@@ -255,30 +255,40 @@ public class MainViewModel : ViewModelBase
         set => SetProperty(ref _defaultStreamVisibility, value);
     }
 
-    public string[] StreamQualities { get; } = { "1080p60", "1080p30", "720p60" };
+    // ─── Resolution quality dropdown (bottom bar) ───
+    // Tiers offered to the creator before going live. First = default. The
+    // dropdown is disabled while live because YouTube stream resolution is
+    // immutable after stream creation (see TASKS.md compliance notes).
 
-    private string _streamQuality = "1080p60";
-    public string StreamQuality
+    public QualityOption[] QualityOptions { get; } =
     {
-        get => _streamQuality;
+        new("1080p60", 60, 8.0),
+        new("1080p30", 30, 8.0),
+        new("720p60", 60, 6.0),
+        new("480p30", 30, 2.5),
+    };
+
+    public string ResolutionHelp { get; } =
+        "Pick the highest resolution your upload bandwidth can comfortably sustain. " +
+        "Find your upload speed on your ISP plan or with a speed test (e.g. fast.com), " +
+        "then choose a tier your upload comfortably exceeds. 1080p60 is the default.";
+
+    private QualityOption _selectedQuality;
+    public QualityOption SelectedQuality
+    {
+        get => _selectedQuality;
         set
         {
-            if (SetProperty(ref _streamQuality, value))
+            if (SetProperty(ref _selectedQuality, value))
                 ApplyStreamQuality(value);
         }
     }
 
-    private void ApplyStreamQuality(string quality)
+    private void ApplyStreamQuality(QualityOption quality)
     {
-        var (bitrate, fps) = quality switch
-        {
-            "1080p30" => (8.0, 30.0),
-            "720p60" => (6.0, 60.0),
-            _ => (8.0, 60.0),
-        };
         var health = CurrentHealth;
-        health.CurrentBitrate = bitrate;
-        health.FPS = fps;
+        health.CurrentBitrate = quality.Bitrate;
+        health.FPS = quality.Fps;
         OnPropertyChanged(nameof(CurrentHealth));
     }
 
@@ -331,9 +341,13 @@ public class MainViewModel : ViewModelBase
 
     public MainViewModel()
     {
+        AppLog.Write("MainViewModel ctor begin");
         _youtubeAuth = new YouTubeAuthService(OAuthCredentials.ClientId, OAuthCredentials.ClientSecret);
         _youtubeStream = new YouTubeStreamService(_youtubeAuth);
         _youtubeChat = new YouTubeChatService(_youtubeAuth);
+        AppLog.Write("MainViewModel ctor: services created");
+
+        _selectedQuality = QualityOptions[0];
 
         _youtubeChat.MessageReceived += OnChatMessageReceived;
 
@@ -369,6 +383,7 @@ public class MainViewModel : ViewModelBase
         _layoutStore = new LayoutStore(DefaultLayoutPath);
         _activeLayoutPath = _layoutStore.ActivePath;
         LoadLayout();
+        AppLog.Write("MainViewModel ctor end");
     }
 
     private static string DefaultLayoutPath => Path.Combine(
@@ -381,6 +396,7 @@ public class MainViewModel : ViewModelBase
         _isLoading = true;
         try
         {
+            AppLog.Write("LoadLayout begin");
             var scenes = _layoutStore.Load();
             Scenes.Clear();
             foreach (var scene in scenes)
@@ -394,6 +410,7 @@ public class MainViewModel : ViewModelBase
                 AddScene("Chat", isChatScene: true);
                 AddScene("Ending");
             }
+            AppLog.Write($"LoadLayout: {Scenes.Count} scenes loaded");
         }
         finally
         {
@@ -402,6 +419,7 @@ public class MainViewModel : ViewModelBase
         ActiveScene = Scenes.FirstOrDefault();
         UpdateActiveBackground();
         ScheduleSave();
+        AppLog.Write("LoadLayout end");
     }
 
     public void Shutdown()

ViewModels/index.md

@@ -0,0 +1,12 @@
+# ViewModels — index
+
+MVVM layer. See [`schema.md`](../schema.md) for the memory-map conventions.
+
+| File | Purpose |
+|------|---------|
+| `MainViewModel.cs` | The app brain: scenes/sources collections + commands, stream state (`IsLive`/`IsOffline`/`IsConnected`), chat feed, overlays, layout save/open, **resolution dropdown** (`QualityOptions`, `SelectedQuality`, `ResolutionHelp`, `ApplyStreamQuality`) |
+| `GoLiveViewModel.cs` | Start Stream dialog: title/description/visibility, start/cancel requests |
+| `ReuseImageViewModel.cs` | Add Image dialog: candidate list (`ReuseImageCandidate`), reuse/new/cancel |
+
+Related: [`Models/index.md`](../Models/index.md) for the data; [`Services/index.md`](../Services/index.md)
+for what the ViewModels drive; base class in [`Helpers/ViewModelBase.cs`](../Helpers/ViewModelBase.cs).